Conventionally, a working gas circulation engine in which fuel, oxygen, and working gas are supplied to a combustion chamber and the fuel is burnt while the working gas in exhaust gas discharged from the combustion chamber is circulated to the combustion chamber through a circulation pathway (circulation passage part) has been proposed. It is also known that it is desirable to use, as working gas, inactive gas with a large ratio of specific heats, such as argon, helium, etc. An engine using such gas with a large ratio of specific heats as working gas may be operated at higher thermal efficiency as compared with an engine using gas with a comparatively small ratio of specific heats as working gas (for example, air, nitrogen, etc.).
In the exhaust gas of a working gas circulation engine as mentioned above, product (hereinafter, may be referred to as “combustion product”; for example, water vapor (H2O), carbon dioxide (CO2). etc.) produced by combustion of fuel (for example, hydrogen, natural gas, etc.) and working gas (for example, argon, helium, etc.) are contained. Among these, especially, water vapor is gas of a three-atom molecule and its ratio of specific heats is smaller as compared with not only inactive gases of a single atom, such as argon and helium, but also air or nitrogen (refer to FIG. 1). Therefore, when exhaust gas containing water vapor with such a low ratio of specific heats is re-supplied to a combustion chamber as it is, the ratio of specific heats as the whole working gas will fall, and the thermal efficiency of the engine will fall as a result.
Then, conventional working gas circulation hydrogen engines are configured so that water vapor (H2O) may be removed from exhaust gas by a condenser and the gas from which water vapor (H2O) has been removed may be re-supplied to a combustion chamber to prevent the ratio of specific heats of working gas from falling (refer to, for example, PTL 1 and PTL 2).